Structural styles and regional tectonic setting of the “Gela Nappe” and frontal part of the Maghrebian thrust belt in Sicily

Abstract

The Gela Nappe of south central Sicily provides an example of a curved segment of an orogenic front that can be examined both onshore and offshore for deformational style and amount of shortening. Synorogenic sediments allow the deformation to be dated. Two distinct structural styles are observed in the Gela Nappe: The central salient part of the nappe (Caltanissetta basin) consists of a single thrust sheet containing a train of continuously tightening folds and the reentrant margins of the nappe (Sciacca and Monte Judica) consist of a stack of several thrust sheets. These different structural styles correspond to the pretectonic Mesozoic stratigraphy of the foreland plate. Carbonate platforms exist on the Adventure bank and Hyblean Plateau ahead of Sciacca and Monte Judica, respectively, while the Caltanissetta basin region appears to have accumulated basinal clay facies. Where the resistant carbonate stratigraphy provides a buttress to the propagation of the thrust front, deformation is taken up by imbrication on‐steep ramps through the carbonates generating a relatively thick orogenic wedge. In the basinal setting, where no strong rheology exists, the low angle of friction on the clay detachment levels requires the growing thrust wedge to be much thinner with a very low foreland dip. Hence the thrust front propagates much farther forward into the basin than it does in the adjacent platformal areas, producing a nonlinear thrust front. In the basinal region, accretion of foreland material to the nappe by imbrication was only prominent during the Messinian when subaerial exposure prevented low‐friction transport of the nappe across the highest levels of the stratigraphy. A steady thickening of the nappe by internal folding suggests an increase in friction along the basal detachment, possibly due to progressive compaction of the clays.

Evidence of positive tectonic inversion in the north-central sector of the Sicily Channel (Central Mediterranean)

“…Moreover, the surface slope of the nappe plunges toward the Gela Basin, contributing to the instability of the sediments resting above the nappe (Fig. 6), as also reported by previous authors (e.g., Trincardi and Argnani 1990;Lickorish et al 1999). …”

“…The south-central area of Sicily is occupied by the Caltanissetta Basin ( Fig. 1) and shows local crustal thinning; this feature, together with the relative low basal friction of the sediment filling the Caltanissetta Basin, favored a major southward advancing of the chain compared to the adjacent higher platform areas, producing an irregular thrust front (Lickorish et al 1999), called the Gela Nappe (Ogniben 1969). Lentini (1982) and Argnani et al (1987) proposed a tectonic push from behind to explain the emplacement of the Gela Nappe, instead of gravitational processes driving a giant debris flow as hypothesized by previous authors (Ogniben 1969;Colantoni 1975;Winnock 1981).…”

Semi-automated extraction of Deviation Indexes (DI) from satellite Persistent Scatterers time series: tests on sedimentary volcanism and tectonically-induced motions

“…The geological setting of this area is controlled by the geodynamic evolution of the Gela Nappe which induces E-W and NW-SE faulting and fracturing in this portion of the Caltanissetta basin (e.g. Lickorish et al, 1999). Indeed, Naro hill shows several well-marked slope changes, morphologic steps and scarps of probable morphotectonic origin oriented along the NW-SE direction, which likely represent the surface evidence of deep-seated tectonic structures.…”

“…The Lower Pliocene marls and marly limestones of the Trubi Formation lie on the Gessoso-Solfifera Formation, are interlayered by the Early Pliocene clays, and covered by Quaternary alluvial deposits (e.g. Lickorish et al, 1999).…”

Integrated geomorphological mapping in the north-western sector of Agrigento (Italy)

“…Along the MaghrebApennine thrust front, the Gela Nappe forms a large arcuate salient and, in the area of Agrigento, has a NW-SE structural trend. Deformation in the basin is dominated by large open folds with 1-3 km amplitude and 5-10 km half wavelength across the general strike; they characterize the geological and structural setting and some of them are cored by southward blind thrusts (Grasso et al, 1995;Lickorish, Grasso, Butler, Argnani, & Maniscalco, 1999).…”